MEXICO CITY — The newly elected mayor of Chilpancingo, Mexico, had appointed Germán Reyes as the man who would safeguard his city.

But on Tuesday, Mexican authorities arrested Reyes, a retired military officer and former prosecutor, accusing him of ordering the mayor’s brutal killing in southwest Mexico last month in a case that had already shocked a nation reeling from widespread violence against local politicians.

The mayor, Alejandro Arcos Catalán, 43, took office in Chilpancingo, the capital of Guerrero state in southwest Mexico, but disappeared less than a week later. On Oct. 6, his head was found on top of a white pickup, local officials said. The rest of his body was in the front seat of the vehicle.

On Tuesday state prosecutors announced the arrest of Reyes, 46, the city’s security chief, on a charge of aggravated homicide, saying he colluded with a local criminal group to abduct and assassinate the mayor.

During a brief recess in court Tuesday, Reyes told reporters that the charge was “absurd.”

— The New York Times